1. Field of the Invention
The present invention relates to a zoom lens system that is suitable for use in an optical instrument such as a digital camera, etc.
2. Description of Related Art
In recent years there has been an increasing need for a zoom lens system in an optical instrument such as a digital camera, etc., to be more compact (miniaturized) and to have a higher optical quality. There is also a very strong demand for miniaturization of the focusing mechanism system and for a rapid focusing operation.
Zoom lens systems configured of a negative first lens group and a positive second lens group, in that order from the object side, are known in the art. A so-called front focusing method, in which the entire first lens group is moved along the optical axis to carry out a focusing operation, is a typical focusing method that is used in such a type of zoom lens system.
However, in such a front focusing method, if the weight of the first lens group, which constitutes a focusing lens group, is large (if the number of lens elements in the first lens group is large), the motor/actuator that constitutes the focusing mechanism system is also enlarged. Accordingly, the diameter of the lens barrel (which includes the zoom lens system of the present invention and the motor/actuator) is enlarged, thereby enlarging the entire zoom lens system.
Japanese Unexamined Patent Publication No. 2004-93593 discloses a zoom lens system configured of a negative first lens group and a positive second lens group, in that order from the object side, in which the two lens elements provided on the image side within the first lens group are used as a focusing lens group.
However, the burden on the focusing mechanism system such as the motor/actuator still remains great, so that such a focusing mechanism system cannot adequately cope with rapid focusing operations.